Only those who smoked the most popular brands in their countries were included in the study, which in the United States included those who preferred Marlboro, Newport, and Camel varieties, according to the study.

"People smoking the U.S. brand cigarettes [we tested] received a level of this carcinogen in their mouth and lungs that was three times higher compared to smokers in Canada and Australia," says Dr. James Pirkle, deputy director for science at the CDC's National Center for Environmental Health.

Eventually, this information may help guide how American cigarettes are made in the future, a practice that thanks to last year's tobacco bill, is now regulated by the Food and Drug Administration.

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"This is important information, I'm confident the FDA will pay a lot of attention to it," Pirkle says.

But American smokers shouldn't run out to buy the foreign brands just yet, tobacco experts say.

"This study should not be taken lightly," says Dr. John Spangler, director of tobacco intervention programs at Wake Forest University School of Medicine, but it only looks at nitrosamines -- "not the two dozen other cancer causing toxins" in cigarettes.

"People might think that by switching brands, they will improve their health outcomes," he says, but it's too early in the research to know whether this might the case.

Smokes Around the World

Why do cigarettes made abroad tend to have lower levels of nitrosamines, or more accurately, tobacco-specific nitrosamines?

According to the study, Australian, Canadian, and U.K. cigarette brands were made from "bright" tobacco, which has a lighter color and uses different curing processes than the U.S. variety.

This means that changes in the variety and preparation of cigarettes can lower the levels of nitrosamine, something Philip Morris, the maker of Marlboro has been aware of for a number of years.

David Sutton, spokesperson for Philip Morris USA, says that the company was able to reduce the levels of this chemical by 80 to 90 percent in the 2002 crop by changing the heating system used.

Unfortunately, making a healthier cigarette is not as simple as lowering the levels of nitrosamines, tobacco researchers note.

"Tobacco smoke contains about 4,000 chemicals," Spangler says, and while lowering carcinogens is likely a step in the right direction, this would not improve "your risk for other tobacco-related diseases [such as] heart disease, stroke, emphysema and many other[s]."